1. Field of the Invention
The present invention relates to a manufacture method of an inkjet printing head, a printing element substrate, and an inkjet printing head by which ink can be ejected.
2. Description of the Related Art
Some inkjet printing heads used in an inkjet printing apparatus use an electrothermal conversion element (heater) for ejecting ink through an ink ejection opening. Such a printing head is configured so that heat generated from the heater can be used to foam ink and the foaming energy thereof can be used to eject ink through the ejection opening.
With an increase of the printing density in recent years, it has been required to arrange a plurality of ejection openings and heaters with a higher density. Japanese Laid-Open Publication No. H11-070658 (1999) suggests a configuration for arranging heaters with a higher density by forming common conductive lines among heaters adjacent to one another so as to reduce the number of the power conductive lines connected to the heaters. A method also has been known to suppress the variation of the volume of ink ejected through an ejection opening by forming a nozzle by a photolithography step on a substrate having thereon a heater. A manufacturing method of a printing head includes the manufacturing method disclosed in Japanese Laid-Open Publication No. H6-286149 (1994). According to the manufacturing method, an ink flow path pattern is formed on a substrate by resin that can be dissolved and the resin is coated with a flow path formation member (covering resin material) including solid epoxy resin at a room temperature. Thereafter, the flow path formation member is exposed and cured to form an ejection opening after which the resin forming the ink flow path pattern is eluted.
FIG. 8 illustrates, as disclosed in Japanese Laid-Open Publication No. H11-070658 (1999), a step in which a flow path formation member 111 made of photosensitive epoxy resin is coated on a printing element substrate 110 to subsequently expose and cure the flow path formation member 111 to form an ejection opening 100. The substrate 110 has thereon a heater 400, an insulating layer 407, an anti-cavitation film 406, and a resin contact layer 405. The substrate 110 also has thereon a common conductive line 401 as disclosed in Japanese Laid-Open Publication No. H11-070658 (1999). The heaters 400 are arranged in the left-and-right direction in FIG. 8. The heaters 400 adjacent to one another have thereamong a part having the common conductive line 401 and a part not having the common conductive line 401. When the flow path formation member 111 is exposed and cured in order to form the ejection opening 100, light is reflected as shown in the arrows in FIG. 8. The arrows A in FIG. 8 show a direction along which ink in an ink flow path 300 is ejected by the heat generated from the heater 400 during the use of the manufactured printing head.
However, when the flow path formation member 111 is exposed and cured as shown in FIG. 8, non-uniform reflected light is caused from a part having the common conductive line 401 among the heaters 400 and a part not having the common conductive line 401 among the heaters 400. Specifically, the existence or nonexistence of the common conductive line 401 at these parts causes different shapes of the insulating layer 407, the anti-cavitation film 406, and the resin contact layer 405. As a result, the reflected lights from these parts have different reflection intensities or reflection angles, which consequently cause a variation in the ejection opening shape of the flow path formation member 111. When the flow path formation member 111 made of photosensitive epoxy resin is subjected to i-ray exposure by an i-ray stepper (i-ray: wavelength 365nm) in particular, there is a risk where the variation in the reflection intensity or the reflection angle of the reflected light may cause the ejection opening 100 to have a distorted shape different from a desired shape. The reason is that the flow path formation member 111 made of epoxy resin is highly influenced by the reflected light because the flow path formation member 111 is photosensitive to i-ray but does not absorb much of i-ray itself.
As described above, the variation in the shape of the ejection opening 100 of the flow path formation member 111 causes a risk of a variation in the ink ejection direction and the ejection amount. This consequently causes a risk where, when such a printing head is used to print an image on a printing medium, the ink landing position on the printing medium is deviated to thereby cause a printed image having a deteriorated quality.